湘东北小坑桥金矿不同地质体稀土元素地球化学特征及其地质意义

Geochemical characteristics and geological significance of rare-earth elements of different geologic bodies of Xiaokengqiao gold deposit in northeastern Hunan

通过对小坑桥金矿不同地质体的稀土元素对比分析,得到以下认识:不同地质体的轻、重稀土比值较高,表明轻、重稀土元素分馏明显;近矿围岩出现明显的负Eu异常;黑云母花岗岩与煌斑岩具有相同的稀土元素特征,认为其可能为同源岩浆产物;金矿体的稀土元素总量与近矿围岩的稀土总量比较接近,表明金矿体继承了围岩的稀土元素组成;金矿体与花岗斑岩均具弱负Eu异常,认为两者很可能在成因上有必然的联系;矿区特征元素与稀土元素的蛛网图显示,Au、As、Sb元素在金矿体中明显偏高,表明Au、As、Sb元素与金的成矿关系密切。综合指出,小坑桥金矿体的成矿物质不仅仅来源于中元古界黄浒洞组地层本身,而且很可能为深部花岗斑岩所提供,其成矿流体很可能为岩浆分异演化的产物,为今后矿区地质勘查工作提供有利依据。

Through comparative analysis on the rare-earth elements of different geological bodies in Xiao-kengqiao gold deposit,the following conclusions can be reached:the ratios of light to heavy rare-earth ele-ments of different geologic bodies are relatively high,which means obvious fractional distillation of light and heavy rare-earth elements;obvious negative Eu anomalies occur in near-ore wall rocks;biotite granite and lamprophyre have the same rare-earth element characteristics,so the authors believe that they are cognate magmatic offspring;the total rare-earth elements of the gold orebody is close to that of near-ore wall rocks, it appears that the gold orebody succeed to the rare-earth composition of wall rocks;weak negative Eu anom-alies occur in both the gold orebody and the granite porphyry,so it is believed that they are inevitably related in respect of genesis;according to the spider diagram of the characteristic elements and rare-earth elements of the mining area,the contents of Au,As and Sb are relatively high,which suggests that these elements are closely related to the gold mineralization.The paper indicates that the ore-forming materials of Xiaokengqiao gold orebody not only come from strata of Mesoproterozoic Huanghudong Formation,but also are likely provided by granite por-phyry in deep part.The ore-forming fluid is likely the product of the differential evolution of the magma.These con-clusions provide a useful basis for future geological survey works in the mining area.